The present invention relates to measurement capable of evaluating poor eyesight by classifying grades of poor eyesight, and more particularly, to measurement which reduces a burden on a test subject.
When illnesses such as pigmentary degeneration of retina and the like become serious and eyesight cannot be represented by a numeral (in which an object of 0.1 at a distance of 50 cm cannot be read), it is evaluated by three steps, that is, by a finger counting test (a test subject counts the number of tester""s fingers shown in front of his or her eyes), a moving finger sensing test (a test subject recognizes fingers moving in front of his or her eyes), and a light sensing test (when a test subject cannot recognize even moving fingers, he or she determines brightness and darkness in a dark room with light irradiated to her or her pupil), based on rational symptom. When a patient of this kind of illness is treated, or when it is intended to evaluate a progress of the illness in detail, evaluation effected at the three steps is too rough to indicate a change of the illness. Further, strong stimulation of eyes with strong light for measurement may damage visual cells.
To cope with the above problem, there is available a measuring method employing a tester using stimulation light emitted from a white LED (for example, xe2x80x9cClassification of Grades of Very Poor Eyesight and Development of Measuring Instrument for Very Poor Eyesight by Hikoshi Kunikata, Masahiro Tsunoda, and Sin Tamai, Journal of Japanese Ophthalmological Society, Vol. 102, extra-edition, p152, 1998). However, the tester has a problem that a large burden is applied to a test subject.
An object of the present invention to accurately measure eyesight of a person having poor eyesight with a small burden on a test subject.
To achieve the object, the present invention is a poor eyesight measuring instrument which is characterized by comprising light emission means for emitting light to each of right and left eyes; light emission control means for controlling the light emission means according to light stimulation steps defined by a combination of light intensities and light emission times; and means for detecting presence or absence of reaction of a test subject to light at the respective stimulation steps, wherein, the light emission control means controls selection of the stimulation steps at random in a series of tests effected a prescribed number of times at each stimulation step; when the light emission control means detects reactions, the number of times of which is a predetermined number of times and less, at a given stimulation step, the light emission control means regards the given stimulation step as not being viewed and omits tests which would be effected at stimulation steps lower than the given stimulation step by a predetermined number of steps; and when the light emission control means detects reactions, the number times of which is a predetermined number of times and more, at a given stimulation step, the light emission control means regards the given stimulation step as being viewed and omits tests which would be effected at stimulation steps higher than the given stimulation step by a predetermined number of steps.
Further, the poor eyesight measuring instrument may comprise means for outputting a total number of the not viewed stimulation steps as an evaluation of poor eyesight.
The light emission means may emit white light and further may emit the three primary colors of red, green, and blue. The light emission means may comprise an LED, a liquid crystal, and a cathode ray tube, and the like. Further, the light emission means further comprises backlight emission means for emitting backlight.
Further, the poor eyesight measuring instrument comprises means for giving a sign, and the light emission control means controls light emission so that light is emitted after a sign is given. At that time, the light emission control means may include control for not emitting light after a sign is given. A sound and other sensible stimulation may be used as the sign.
A method effected by the instrument is also included in the present invention.